From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755859AbaEGLO2 (ORCPT ); Wed, 7 May 2014 07:14:28 -0400 Received: from mail-ee0-f46.google.com ([74.125.83.46]:36033 "EHLO mail-ee0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755316AbaEGLO1 (ORCPT ); Wed, 7 May 2014 07:14:27 -0400 Date: Wed, 7 May 2014 13:14:22 +0200 From: Ingo Molnar To: Andy Lutomirski Cc: Linus Torvalds , Thomas Gleixner , Linux Kernel Mailing List , the arch/x86 maintainers , Steven Rostedt , Gleb Natapov , Paolo Bonzini Subject: Re: [ABOMINATION] x86: Fast interrupt return to userspace Message-ID: <20140507111422.GA8410@gmail.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Andy Lutomirski wrote: > > Whatever. I got enough profile data to say that it seems to have > > cut 'iret' overhead by at least two thirds. So it may not *work*, > > but from a "hey look, some random numbers" standpoint it is worth > > playing with. > > :) > > Is there actual interest in turning something like this into a real > patch? It would almost certainly have to default off and no one > sane would ever use it except for special-purpose machines. The macro speedup looks rather impressive, and we've done ugly things for far smaller speedups. But I don't think it should be a 'special mode'. It either is made to work unconditionally and can be a prime speedup to be proud of in a politely disgusted fashion, or we don't want the complexity (and future bitrot) of some special switch. At minimum it can be a "look we want this speedup in hardware" testcase to CPU designers. Thanks, Ingo